The present invention relates in general to electron discharge devices and more particularly to a traveling-wave tube including electronic circuitry so that no adjustment is required in the field to provide the voltage necessary for proper operation of the traveling-wave tube.
Many complex electronic systems utilize one or more electron discharge devices as traveling-wave tubes and, in general, these traveling-wave tubes are field replaceable; i.e., a tube is replaced directly in the field whenever it fails to meet specifications. However, because the performance of a travelling-wave tube, particularly a low noise traveling-wave tube, is critically dependent upon the high electrode voltages, typically in the range of thousands of volts, supplied by the system's power supply and because it is not unusual to find the regulation of the system power supply just barely within the regulation limits permitted by the traveling-wave tube specifications, operation of the traveling-wave tube within specified performance can be achieved only if the error in setting electrode voltages is extremely small. A typical cathode helix voltage regulation specification for a low-noise traveling-wave tube with a helix slow-wave structure is at most .+-.0.5 percent.
Presently, one common method in field adjustment of low-noise traveling-wave tubes is to adjust the cathode-to-helix voltage for optimum small signal gain at the highest operating frequency. This method has the advantage of not requiring an accurate voltmeter since the voltage is not even measured; however, it does require much more skill in setting the voltage. Furthermore, the design of equipment may require certain modifications to permit a small signal gain measurement. Another difficulty is that many low-noise traveling-wave tubes exhibit optimum performance at a voltage different from that producing maximum gain at the highest operating frequency. Finally, this procedure does not provide a method for accurately setting the various anode voltages, necessary in low-noise traveling-wave tubes, without use of an accurate voltmeter which has a very high internal impedance.
As a general rule voltmeters with the required accuracy for setting the electrode voltage are not available in the field. Therefore, optimum performance is seldom achieved in replacement traveling-wave tubes. Even when accurate voltmeters are available in the field, they require frequent calibration checks which are often logistically impossible. Additionally, required accuracy is difficult to achieve even if the particular meter setting happens to be a full scale reading, and danger to the operator exists in setting up such a meter to read a high voltage.
Coupled with the problem of proper setting of the cathode-to-helix voltage in low noise traveling-wave tubes is the setting of various anode voltages for multiple anode electron guns present in all low noise traveling-wave tubes. The required anode voltages are determined by the particular design of the low noise gun. Because of manufacturing tolerances there is rather a wide variation in anode voltages from tube to tube, but the tolerance within which these voltages must be set in order to achieve the desired noise figure is only about .+-.1.0 percent of the nominal values. Thus, the problems encountered in setting the anode voltages are similar to, and as difficult as, those encountered in setting the cathode-to-helix voltage.
In another prior art system a voltage bridge network is connected within the traveling-wave package between the cathode and slow-wave structure of the traveling-wave tube. The bridge network is adjusted by the manufacturer such that a reading can be made in the field across the bridge of the bridge network, and the voltage applied between the electrodes adjusted until a null reading exists in the measuring device. At this point a desired predetermined voltage exists between the electrodes. Such a system is more fully described in a pending patent application entitled "Electron Discharge Device with Integral Voltage Bridge and Method of Setting Same," filed Feb. 3, 1969, Ser. No. 796,133, by James L. Palmer and G. E. Tallmadge, and assigned to the assignee of the present invention. Such a system, while an improvement over the previously described prior art system, still has the significant disadvantage that a null reading must be taken to provide the proper voltage setting and complete interchangeability of tubes and supplies without adjustment is not possible.